1. Field of the Invention
The present invention relates to a method for diagnosing gastrointestinal disorders. The invention also relates to a method for measuring dissolved inorganic carbon (DIC) in biological fluids.
2. Description of the Prior Art
Among the chronic disorders of the upper gastrointestinal tract are those which fall under the general categories of gastritis and peptic ulcer disease. The upper gastrointestinal tract is generally defined as including the esophagus, the stomach, the duodenum, the jejunum, and the ileum. Peptic ulcers are lesions of the gastrointestinal tract lining, characterized by loss of tissue due to the action of digestive acids and pepsin. It has been generally held that peptic ulcers are caused by gastric hypersecretion, decreased resistance of the gastric lining to digestive acids and pepsin, or both. Gastritis is, by definition, an inflammation of the stomach mucosa. In practice, though, the disorder is manifested by a broad range of poorly-defined, and heretofore inadequately treated symptoms such as indigestion, "heartburn", dyspepsia and excessive eructation.
Helicobacter pylori (HP) is a curved Gram-negative rod which colonizes gastric mucosa and is etiologically associated with histologic gastritis. HP has been isolated from gastric mucosa by histology and culture in 25 to 36% of asymptomatic populations, in 83% of persons with duodenal ulceration, and in 77 to 100% of patients with chronic active gastritis. Diagnosis of HP infection has traditionally been made by endoscopy and biopsy.
Because the most distinctive characteristic of HP is the production of highly active urease, urease tests and urea breath tests have been increasingly utilized recently for the diagnosis of HP infection. The CLOtest, such as described by Morris, A., et al., Lancet, 1:149 (1986), is a commercially available test for the colormetric detection of urease activity in endoscopic biopsy specimens.
Diagnosis of t IP infection may also be conducted by IgG or IgA antibody serology as described by Evans, DJ. et al., Gastroenterology, 96:1004- 8 (1989). Serologic screening for IgG or IgA antibodies to HP does not provide reliable information because antibody titers against HP tend to fall slowly over several months after successful antibacterial therapy, and generally remain in the abnormal range after therapy.
Diagnosis may also be made by the CO.sub.2 breath test as described in U.S. Pat. No. 4,830,010. The breath test is conducted by administering urea to a subject and measuring CO.sub.2 released. The urea may be isotope-labeled with .sup.13 C or .sup.14 C. Urease catalyzes the release of CO.sub.2 from urea. CO.sub.2 released from urea by urease may be found in several dissolved inorganic carbon (DIC) forms in tissues. These DIC forms are carbonate (CO.sub.3.sup.=), bicarbonate (HCO3.sup.-), carbonic acid (H.sub.2 CO.sub.3) and dissolved CO.sub.2. Although the CO.sub.2 breath test provides a noninvasive form of diagnosing HP infection, the method requires specialized collection and transportation apparatus, usually requires 50 cc of exhalate, and is time consuming. When .sup.14 C is used, the CO.sub.2 breath test necessitates a small amount of radiation, which precludes its use in pregnant women and small children.
A method for measuring DIC in body fluid samples has not heretofore been described. Current methods for measuring forms of DIC include physical techniques such as Natelson microgasometry and enzymatic methods based on phosphoenolpyruvate carboxylase (for measuring bicarbonate). These methods are unsuitable for detecting DIC elevations in body fluids caused by bacterial urease activity. Thus far, extraction of blood .sup.13 C-bicarbonate had been difficult because, upon contact with a mineral acid, blood coagulates and impedes the liberation of CO.sub.2 from the sample.
These and other disadvantages of the prior art are overcome by the present invention, and a new method for measuring DIC and for diagnosing or monitoring gastrointestinal disorders is provided.